Tuesday, December 20, 2011

Last summer, we bought a used Elec-Trak tractor -- I suppose "used" is a bit redundant since the last Elec-Trak left the factory in the 80's.

Our "new" Elec-Trak after some TLC.

The Elec-Traks are all electric tractors powered by a set of on-board lead acid (golf cart) batteries. They were made by GE for several years during the 70's, and were popular with more than 30,000 made. They are very durable and functional machines with a wide range of all electric accessories. The Elec-Traks have a strong following with an online owner forum and good parts support. Many of these tractors have been rebuilt and are serving people well. Being electric, these machines are cleaner, cheaper to run, and low maintenance than equivalent gasoline models.

The Elec-Trac with new charger/inverter supplying 120 VAC power out in the field.

In addition to the usual mowing and snow blowing tasks, we wanted to be able to use the Elec-Trak to power our home during power outages -- it has a large enough battery pack to power a few critical loads like the fridge and furnace for something in excess of a day. This proved to be a relatively easy thing to do using a commercial charger/inverter from Tripplite.

In addition, we wanted to work out a way to use our grid-tied PV array to charge the Elec-Trak battery pack during power outages. This proved to be more of a challenge in that grid-tied PV arrays are designed to stop operating as soon as a power outage is detected, and to stay offline until the grid comes back. After a bit of head scratching, we did work out a way that is fairly easy and effective if not terribly elegant. The nice thing about our arrangement is that we get most of the benefits of a grid-tied with battery backup PV system, but without the considerable initial expense of these systems and without the need to maintain and replace a set of batteries that is almost never used. See the link below for details.

Charging the Elec-Trak batteries during a simulated power outage using our PV array.

Friday, December 16, 2011

Bright Harvest offers a somewhat unique solar site survey. They use aerial photos of your house to build a digital model, and then show you alternative arrangements of collectors. They also model any shading objects near your home, and show the monthly and yearly effect of this shading on the output of the array. Estimates for yearly output are also shown.

Overview of the model and panel layout with shading.

They offered to do a survey of my house, and I took them up on this and the link at the bottom of this post is to a page with the details on the survey and some thoughts on it.

In a nutshell, I was favorably impressed by the survey. They did a good job of identifying potential PV array placements and a good job of finding shading sources. Even though I've done a couple "manual" solar site surveys on my home myself, they found some things that I had missed or not thought about.

The cost of the survey is not trivial at $150, but it may well be worth it to get a good handle on shading -- especially for complex situations.

I would always recommend doing the "manual" solar site survey yourself, as it will make you aware of how the sun interacts with the house and shading objects over the course of the year -- its just something everyone should do before tackling any solar project. But, if you are uncertain about the shading situation or array mounting possibilities after the manual survey, the Bright Harvest survey or a SketchUp model would be a very good follow up. I get a lot of emails from people who put their collectors up, and then come to find that the shading situation is worse than they thought -- it is just very important to have a good handle on shading before starting.

Monday, December 12, 2011

Randy made the machine to make it easier to do the planting, weeding and picking chores in the garden. The seats on each side are adjustable side to side to accommodate wide or narrow rows of plants. The speed control is a joystick that can be mounted left, right or center.

The frame is made from 1 inch welded steel tubing. It is solar powered using 4 golf cart batteries and two on board 80 watt PV panels that also provide shade for the driver.

The drive train is from an electric wheelchair, but is geared down for more torque. Maximum speed is about walking speed.

Friday, December 2, 2011

Greenstar Blox are a new wall building product that has been under development for several years. The Greenstar Blox offer the promise of high strength, durability, high R values, reasonable cost, and a relatively straight forward build process. It looks to me like they might make a good material for owner built homes.

A Greenstar Blox project

The standard Greenstar Block is 10 by 14 by 4 inches and is made from roughly 65% selected recycled paper, 25% Portland cement, and various additives. This is similar to papercrete, but the difference is that Greenstar Blox are commercially made to a standardized recipe using a standardized process to produce a consistently high quality block. The Greenstar Bloxs are currently going through an extensive testing program at Texas Tech University. The results of the testing program are being used to seek building code approval, which is anticipated in early 2012.

The blocks are laid in courses as usual (kind of like Legos). The mortar is made from the samematerial that the blocks are made from.

The blocks appear to be relatively straight forward to build with. They are much lighter and easier to handle than concrete blocks. They offer the big advantage of a high R value right in the block without the need for additional layers of insulating material. Greenstar says that walls made with their blocks will be about R25.

An important item for anyone thinking about building with these blocks is that building code approval is in the works -- this will make it much easier for people wanting to build to get building permits.